As it turned out, the economist, Guido Menzio, whom Rampell described as having "dark, curly hair, olive skin, and an exotic foreign accent," had been working on a math equation.

After an attempt at small talk, a 30-year-old female passenger, whom American Airlines has not identified for privacy reasons, alerted a crew member, and Menzio was taken off the plane for questioning.

Menzio showed his notes — a differential equation he had been working on for a speech he was traveling to give at Queen's University in Ontario, Canada — to the authorities and was allowed to reboard the plane and return to his seat.

Menzio was "treated respectfully throughout," he told Rampell, but was frustrated that such an incident could happen.

He also believes that a xenophobic undercurrent in American politics contributed, later adding, "It is hard not to recognize in this incident, the ethos of [Donald] Trump's voting base."

The female passenger never returned to her seat.

The Department of Homeland Security encourages passengers to remain aware of their surroundings and inform airport personnel of behavior they see as suspicious with its "If you see something, say something" mantra.

Menzio is a well-regarded economist who last year won the Carlo Alberto Medal, an award given to the best Italian economist under 40. He is a tenured associate professor at the University of Pennsylvania.

"Whenever there are conflicts between passengers we try to work with them peacefully to resolve it," Casey Norton, a spokesman for American Airlines, told Rampell.